I’ve tested lots of 70 or 75-300mm tele zoom lenses over the years and they’ve all showed more or less the same characteristics - good to great at the short end - poor to awful at the long end of the zoom range.
Tamron is a name I have great respect for - they make some great lenses, and the Tamron 70-300mm LD, although very reasonably priced, gives some very much more expensive lenses a run for their money.
Of all the Sigma, Canon, Nikon, Tokina and Pentax something to 300 zooms I’ve used - The Tamron, while not really sparkling anywhere, is completely useable at all focal lengths even at full aperture. This might not sound like much of a recommendation, but it’s a crucial difference. Although, the Sigma APO in particular is superb at 70mm it is just OK.. ish at 300mm, as are most of the others.
Despite it’s very lightweight price and mostly plastic construction the Tamron 70-300mm LD doesn’t leave you feeling short changed, as it does have a metal mount and the lens hood is included in the price. (are you listening Canon?) This is a good rather than great lens. Not simply stunning anywhere - like the Sigma APO at 70mm - but not terrible anywhere either. Stopped down even to f8 performance is very good indeed at all focal lengths. That coupled with it’s light weight and low price make the Tamron 70-300 LD a much better holiday choice than many more expensive and heavier alternatives.
Nikon Users: If you own a newer Nikon such as the D3000, D3100 or Nikon D5000 check for compatibility. See the notes at the bottom of the Nikon Lenses page